Two-step colloidal synthesis of micron-scale Bi_(2)O_(2)Se nanosheets and their electrostatic assembly for thin-film photodetectors with fast response

Recently discovered bismuth oxychalcogenide(Bi_(2) O_(2) Se) has aroused great interest due to its ultrahigh carrier mobility,tunable band gap and good environmental stability,making it a promising candidate for high-performance electronics and optoelectronics.Their synthesis by colloidal approaches represents a cost-effective alternative to well-established chemical vapor deposition methods,and the resulting electronic-grade inks are important for large-area printed or wearable electronics.However,it is still challenging to control the colloidal growth of Bi_(2) O_(2) Se nanosheets in solution in addition to their assembly into high-performance thin films.Here,we report a two-step colloidal synthesis of Bi_(2) O_(2) Se nanosheets by separating the seeding and growth steps,thereby achieving controllable production of nanosheets with a lateral size of 1.4 mm and a thickness of 10 nm at optimized reaction conditions.These Bi_(2) O_(2) Se nanosheets are electrostatically assembled into large-area thin films,from which a photodetector is fabricated with a responsivity of 6.1 A/W and a short response time of 368 ms under the 520-nm laser illumination.The device exhibits fast response to modulations as high as 100 k Hz,along with a à3 dB bandwidth of 1 kHz.This work provides an important understanding of the controlled colloidal synthesis of Bi_(2) O_(2) Se nanosheets,and demonstrates their potential applications in fast photodetectors.